The use of automated or driverless vehicles is becoming more widespread. Such vehicles are commonly used in a variety of industrial settings, where it is desired to have one or more vehicles travel a set route, or defined network of routes. In such situations, automated vehicles offer considerable advantages and cost savings.
By automating vehicle operation, the cost of having an individual operator for each vehicle is avoided. Where the vehicles are repeatedly traversing relatively short routes, this is tedious for the operator, and operator boredom and fatigue can be a problem. By automating guidance of the vehicle, in many cases, the vehicle can be guided more consistently and accurately, and this can be useful in environments where there are tight clearances.
Such automated guidance systems have been developed for use in factories and the like. To keep the design of the guidance system simple and robust, a common element of most systems is to provide some clear indication of the path or route along which the vehicle is to travel. This avoids having to provide the vehicle with any complex computer system, artificial intelligence or the like, which enables it to determine the route to take.
In factories and the like, defining a route for the vehicle is a relatively simple matter. More importantly, the route or routes are usually fixed or set, and it is simply a matter of making a single installation of some device marking the route. One known technique is to provide a wire or cable embedded into the floor of a factory. A guidance system then uses the electromagnetic characteristics of this cable to guide the vehicle so that the vehicle follows the path of the cable. It is also known to use optical techniques and a strip painted on the floor.
More recently, there have been proposals to provide such automated vehicle guidance systems for use in a mine. A mining environment poses a wholly different set of problems from a conventional industrial setting. Firstly, the whole environment is much harsher than a conventional factory. Frequently, there are high levels of dust, and any path or route rather than being along a smooth, concrete floor or the like may well be a long rough floor of a tunnel or drift.
Additionally, in a mine, there are problems of electrical power supply. Again, in a conventional industrial plant, electrical power is usually readily available.
A further factor is that, in a mine, by its very nature, the pathways of the vehicle are irregular and subject to constant change. In a factory setting, the initial installation cost of the system defining the route or path of the vehicle is not usually critical, since it is a one time cost. In a mine, on the other hand, where the route or path must be constantly changed and updated, the cost of installing devices or equipment to define the route is an extremely important factor.
Nonetheless, despite these numerous differences between an industrial setting and a mining environment, many guidance systems proposed for mines make little or no allowance for these differences. Thus, one technique is to borrow the optical guidance technique used elsewhere. It is recognized that providing some sort of path along the floor of a drift is impractical in mind, and it would often be subject to severe damage or simply covered in debris.
Instead, it has been proposed to provide an elongate reflective strip suspended above the desired path for a vehicle. Such an arrangement is taught in Canadian Patent 2,041,373 (Mintronics Systems Corporation). This provides a so-called coded longitudinal reference means, which more specifically is retroreflective. There are various proprietary tapes available which provide such retroreflective capability. While this solution may appear relatively simple and practical, it does not totally solve all of the problems. The strip itself still needs to be hung at regular intervals, and must be oriented downwardly to a reasonable degree of accuracy.
The intention is that the reflective strip would be detected by lasers. The lasers are oscillated from side to side, and the position of the laser is noted when a beam is returned to the vehicle.
However, this arrangement has numerous disadvantages. Firstly, it requires lasers and a relatively delicate mechanism for causing the lasers to oscillate. Providing such a mechanism that is robust enough to withstand the typical working conditions of a mine is extremely difficult, and many mechanical failures have been encountered.
A more significant problem is that a retroreflective strip does not, in fact, provide an adequately bright return signal to enable it to provide a positive and accurate guidance system for the vehicle. In particular, as a vehicles speed increases, it is standard practice to cause the guidance system to look further ahead, so as to anticipate turns in the path.
In a mine, a drift will have the minimum height possible, so that a laser has to be shone forward so that is strikes the reflective strip at a fairly shallow acute angle. This in turn gives a poor reflected signal. Additionally, mine environments are typically cluttered. Along many drifts or tunnels, there are numerous other linear objects, e.g. pipes, duct work, cabling etc, all of which are capable of acting in a reflective manner. It is therefore quite easy for the guidance system to be confused by all the other objects suspended from the roof of a drift, which provide background clutter.
This problem has been recognized, and others have proposed solutions to it. In particular, Canadian Patent Application 2,145,731 discloses an automated guidance system for a vehicle which provides a continuous source of light arranged parallel to the intended path and above the vehicle. Such a source of light can be what is known as a "light rope". This is a commercially available product comprising numerous small bulbs encapsulated to form, in effect, a continuous rope or string.
This system certainly has a number of advantages. It provides a continuous, bright source of light, which is easily recognised by a vision and guidance system. It avoids all of the problems of interference by reflectance from background objects.
However, such a system is extremely costly both to install and to maintain. At current prices, it can cost around C$10.00 per foot and requires about 5 W of power per foot. In one large installation of which the applicants are aware, the installation cost was of the order of $300,000.00, and the completed installation required 100 kW of power.
Providing power at this sort of level down a mine is extremely difficult, complex and costly. In sizable installations, it results in strategies requiring sections of the available routes to be turned on and off as required, so as to minimize power requirements. This leads to complications, and stranding of vehicles, if the power is accidently turned off. It imposes a significant maintenance burden, since the light rope must be monitored, and sections replaced as bulbs fail.
To this end, to maximize the life of the light rope, some unusual precautions are taken. The voltage is reduced. Additionally, it has been discovered that in a blasting environment, the bulb filaments are much more robust when warm and much less susceptible to failure, so that the lights are maintained switched on when blasting occurs.
As noted, by its very nature, a mine environment requires continuous creation of new drifts and routes, and closure of old ones. This requires constant installation and removal of a guidance system. Where this light rope system is used, this requires the light rope and associated transformers, power supplies etc., all to be moved and relocated.
This light rope approach has enjoyed some considerable commercial success, but this only serves to underscore the limitations of the retroreflective tape approach. What is really required is some technique for defining a route for a vehicle in a mine, or other environment, which enables a route to be quickly and accurately defined, which is inexpensive to maintain and install, and which ensures accurate tracking of the route by a vehicle.